Foam Board Insulation R Value Chart and Types

Home insulation is necessary for any cool & warm regions! It moderates room temperature efficiently. Also, cuts down costs at times. Considering using foam board insulation for home? Looking for a good R value? Well, you will get answers to all your questions.

Just go through this quick guide. We have told Foam board insulation types, R-value charts (by type & per inch), how to choose the best foam board insulation, and similar. Come on, let’s get into the post. You’ll be enriched with knowledge in a few minutes.  

Foam Board Insulation R-Value Chart

R-value tells how well a foam board insulation can hold conditioned air. Be it heat or cool air. In technical terms, R value is the measure of resistance to the flow of heat. The higher the R value of foam board, the better is the material’s holding capacity and vice-a-versa! It’s not about how much heat a form board absorbs, rather how much it HOLDS! So, it keeps the house conditioned for that long time.

Foam Board Insulation R-Value Chart

Foam Board Insulation R-Value Chart by Type

There are many kinds of foam board insulation. All of them have a unique R-value. Let’s look into these foam board insulation R value:


R Value


4 to 6.5 per inch of thickness

Polyisocyanurate (ISO)

7.0 to 8.0 per inch of thickness

Extruded polystyrene foam (XPS)

4.5 to 5.0 per inch of thickness

Expanded polystyrene foam (EPS)

3.6 to 4.0 per inch of thickness

As you can see, R values of rigid insulation are higher while spray foam r value is lower.

Remember ! : Foam board insulation R value isn’t the only thing to consider before buying. The thickness also matters! A 6 inches of poor-quality foam board insulation can have higher R-value than 1 inch of high-quality foam board.

So, consider the below information too.

Foam Board Insulation R-Value per inch

Here is a polyiso rigid insulation R-value chart. The r value increases as thickness improves.

Thickness (in Inches)

R-value (in I-P/Imperial)

RSI (R-value in Metric)































Foam Board Insulation Types

There are basic three foam board insulation types. In the market, you’ll find only these 3 insulation foam boards under different manufacturer names.

Foam Board Insulation Types


Polyurethane foam is created by reacting polyols and diisocyanates which are obtained from crude oil.

Polyurethane is available as rigid boards and spray foam both. You can use rigid board sheets especially in new constructions.

Rigid Polyurethane Foam

These pre-made panels are great for insulating unfinished walls, exterior wall insulation, basement wall insulation, rim joists, and foundation walls. Also, these boards are good for building privacy walls. You can cut the panels and fit into main building areas.


  • It has higher R values ranging from 4 to 6.5 per inch because of rigidity
  • It is water-resistant so best to avoid water-leakage, mould, & rot
  • High thermal-bridging capacity. Prevents loss of heat over time
  • Excellent air-barrier
  • High Durability, almost up to 100 years or more, does not sag over time
  • Perfect for colder and damp regions
  • Yields lower utility bills


  • Expensive
  • It is flammable
  • Can damage when exposed to UV-rays
  • Difficult & time-taking installation process. Joints must be fitted tightly to avoid air infiltration
  • Not ideal for insulating hard-to-reach spots & crannies

In a nutshell, you’re sure to get the racking strength to your walls!

Polyisocyanurate (Polyiso/ISO)

It is available only as rigid insulation foam boards. These ISO panels are faced with foil. The foil is water-impermeable as it forms an external vapour barrier. It has the highest R value as per rigid insulation R-value chart. Generally, r value per inch is high in case of Polyisocyanurate rigid boards.

Remember ! : Never use ISO foil panels with internal vapour barrier. If done, the air gets trapped between two barriers, creating mould & mildew.

You can use this rigid insulation on roofs with hot asphalt. It is popularly used on commercial roof constructions.


  • It has the highest R value of 6 to 6.5 as per rigid insulation R-value chart
  • Suitable for temperature range up to -100 degrees fahrenheit to +250 degrees fahrenheit
  • It has low water-absorbency and low vapour-transmitting power
  • It is unaffected by insecticides, fertilisers, and other oil-based waterproofing compounds
  • Polyiso has zero global warming and ozone depletion potential


  • Expensive when compared to EPS or XPS
  • Polyiso doesn’t work well in temperatures below 50 degrees fahrenheit
  • Least eco-friendly alternative when compared to EPS or XPS
  • High thermal drift or loss of heat over time

Extruded polystyrene foam (XPS)

Extruded polystyrene  Rigid Foam

XPS is a styrofoam. It is a tightly-packed closed-cell insulation. Made of 98% air and 2% plastic, it is 100% recyclable but not biodegradable. It is available in colours like pink, blue, and green. You can use XPS below-grade, below the slab, and on basement walls. 


  • XPS has an foam board insulation R value of 5
  • It is cheaper than Polyiso but expensive than EPS
  • It is more moisture & mildew resistant than EPS. Perfect for wetter and rainy regions.
  • It has high compressibility when compared to EPS
  • No thermal drift or loss of heat over time
  • 100% Recyclable


  • It attracts ants & termites
  • It is flammable

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Expanded polystyrene foam (EPS)

It is the cheapest insulation of all but also has a lower R value. The EPS beads are closed-cell. They are available as rigid blocks and sheets. Made of 98% air and 2% plastic, it is 100% recyclable but not biodegradable. You can use EPS on roofs, walls, floors, below-grade, etc. Moreover, one can use it for vinyl siding, concrete foams, ICF blocks, SIPs, in ELFs, etc. Besides, it is also used as food containers.


  • It has an R-value of 3.18 to 4.6
  • No thermal drift or loss of R-value (loss of heat) over time
  • No off-gassing
  • As it is water-impermeable, EPS is mould and mildew resistant


  • It attracts ants & termites
  • As there are fewer air spaces, water can penetrate inside it
  • It is flammable

How to choose the right type of rigid foam for your needs?

You can buy foam insulation at the local home depot. But, how do you choose most-right foam board insulation for your house? Here we get you through the buying guide in the next few minutes. 

Pro-Tip : Always carry a Knife as you go to the local home depot. If insulation boards are too big, cut them into small pieces to carry home.


It’s the prime factor – Price! You have to decide how much you are willing to spend on insulation. Are you looking just for insulation or further renovating too? Accordingly, your price budget will be more or less. Based on your pricing budget, you can insulate EPS, XPS, or Polyiso.

A foam insulation type also differs based on weather climate. A polyurethane rigid foam is ideal for damp & high humidity regions as it avoids moisture and thereby mould & mildew. EPS is also good in this case if you’re looking for a cheaper option. It too prevents moisture but has also a lower R value.

So, if you’ve a high price budget, go for polyiso, polyurethane or XPS. If you’re low on budget, go for EPS.

Ease of Application

Are you on your toes to insulate your house? If you’re an enthusiastic crafty homeowner, you will do so. However, be cautious while you use the insulation type!

Fibreglass insulation is often harsh on human skin. Rather, only use foam insulation. Make sure that you use a protective shield, mask, gloves, and clothing while doing so to avoid cuts or exposure to chemicals.

Rigid polyiso and extruded boards are a bit trickier to install. You need to cut the sheets or boards in bigger or smaller sizes as per requirements. It’s easy when using a high-utility knife to do so. Though utility differs for all kinds of foam insulations!

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Place where you apply foam insulation

The type of foam insulation you will select also depends on space! In other words, where will you apply foam insulation?

A rigid foam board is ideal for unfinished walls, foundation wall insulation, floors & ceilings, and non-vented low-slope roof areas.

For unfinished attic insulation, you can use polyurethane foams. These rigid board insulations are easier to install in newer constructions. Fixing rigid boards in existing building constructions is a bit tricker! 


Lastly, durability is king! You’re taking on an insulation hurdle for just once! Consider your home interiors, weather climates, and areas like crawlspace, basement, attics, basement, floors & ceilings, etc where you will insulate. With proper home insulation evaluation, you can install the right insulation. It will surely go longer.

What rigid insulation has the highest R-value per inch?

Polyisocyanurate (Polyiso/ISO) rigid insulation has the highest R value per inch. It approximately ranges between 6.5 to 6.8. Also, generally, R values of rigid insulation are high. It generally has a foil facing on one side. While insulating the home one side, it adds a finished appearance to the place as well.

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Final Thoughts

Foam board insulation are clever ways to insulate your home externally and internally! It truly does a great job. Though there are several foam board insulation types, choose one that fits in your needs & budget.

Lastly, remember, R value of foam board is important while selecting foam board insulation. Yet, air sealing properties, water & mildew resistance, thermal drift capabilities, etc are also relevant. Consider all factors to get the best deal of all times!

Also, refer to the above short post to get clever clues.

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